How to save a PowerPoint presentations’s template

One solution is to use a macro-enabled template (dotm) with a VBA macro to replace SaveAs.

An example macro is:

Public Sub FileSaveAs()
    Dim dlg As Dialog
    Dim strSaveFolder
    strSaveFolder = Application.Options.DefaultFilePath(wdDocumentsPath)
    Select Case ActiveDocument.AttachedTemplate.Name
        Case "Woodworking.dot"
            Application.Options.DefaultFilePath(wdDocumentsPath) = "C:\Woodworking"
        Case "Travel.dot"
            Application.Options.DefaultFilePath(wdDocumentsPath) = "C:\Travel"
    End Select
    Set dlg = Dialogs(wdDialogFileSaveAs)
    dlg.Show
    Application.Options.DefaultFilePath(wdDocumentsPath) = strSaveFolder
End Sub

You will still need to attach this macro to Ctrl-S.

If you use a separate template document per user, the above "Select Case" can be simplified to a simple assign in each of the templates.

source

View as "slide masters". When you mouse over each slide master, you can see if that slide master is used. You can individually delete each slide master. Looks especially for those with pictures and remove the ones not used.

If you highlight the first slide, then keep hitting Delete repeatedly, only the slide templates that are not in use will be deleted. This is an easy way to manually roll through the templates quickly without worrying about removing one that is in use.